1. Field of the Invention
The present invention relates to a photo film take-up spool and shaft. More particularly, the present invention relates to a photo film take-up spool and shaft for winding photo film to be used in a lens-fitted photo film unit.
2. Description Related to the Prior Art
A lens-fitted photo film unit is pre-loaded with unexposed photo film of a 135 type, and operable for taking exposures in a manner of a camera. The lens-fitted photo film unit includes a cassette containing chamber and a photo film roll chamber between which an exposure aperture is disposed. The cassette containing chamber contains a cassette shell of a photo film cassette. The roll chamber contains a roll of the unexposed photo film drawn from the cassette shell. Two types of lens-fitted photo film units are known: a two-spool type and a one-spool type. The two-spool type includes a cassette spool and also a take-up spool about which the roll is formed by winding the photo film. The one-spool type includes a cassette spool but not a take-up spool. An apparatus for producing products of the one-spool type includes a take-up shaft, about which a roll of photo film is formed by winding the photo film in a factory. The take-up shaft is moved into the roll chamber, places the roll in the roll chamber, and moved away from the roll chamber, to load the lens-fitted photo film unit with the roll of which the center does not have a spool.
U.S. Pat. Nos. 4,884,087 and 4,954,857 (corresponding to JP-A 64-544) discloses a photo film take-up shaft in which a take-up slot is formed longitudinally and openly at a distal end thereof. A pressing spring plate is disposed inside the take-up slot, to nip a leader of photo film between the spring plate and a confronted wall inside the take-up slot. The take-up shaft is rotated to wind the photo film in a roll form thereabout. JP-A 5-204094 discloses a photo film take-up spool in which a take-up slot is formed longitudinally. Hooks are formed on the inside of the take-up slot. Perforations are formed in a leader of photo film, and engaged with the hooks. The take-up spool is rotated to wind the photo film thereabout.
In a lens-fitted photo film unit, photo film is moved into a cassette as much as one frame each time an exposure is taken. When a final frame is exposed, the photo film is wound to include the entirety of the photo film having the leader into the cassette. If the lens-fitted photo film unit is a two-spool type, the leader is smoothly detached from the take-up spool after the exposure on the final frame. The lens-fitted photo film unit is forwarded to a photo laboratory, where the cassette is removed. The photo film as exposed is removed from the cassette, and is developed and subjected to printing, by techniques known in the field of the photo finishing.
U.S. Pat. No. 4,832,275 discloses a photo film cassette in which a leader of photo film is pre-contained entirely in a cassette shell and rotation of a spool in an unwinding direction causes the leader to advance to an outside. The photo film contained in this includes a support and an emulsion layer formed thereon. The support is formed of annealed polyethylene naphthalate (A-PEN) having great rigidity and advantage of great easiness in advancement of the photo film. The photo film has the leader, an effective exposure area and a trailer. In the effective exposure area, two perforations are associated with each of frames. No perforation is formed in the leader or the trailer.
However the take-up spool or shaft disclosed in JP-A 5-204094, having the hooks for engagement with perforations in the leader of the photo film, cannot be used with the photo film in which no perforation is formed in the leader.
The take-up shaft disclosed U.S. Pat. Nos. 4,884,087 and 4,954,857 (corresponding to JP-A 64-544) is usable in fashion irrespective of existence of perforations. However a shortcoming lies in that an irrecoverable fold is inevitably formed in the photo film leader in an edge position between the take-up slot and a cylindrical face of the spool core. Once folded, the highly rigid photo film cannot recover its original condition without the fold. If the suggestion of U.S. Pat. Nos. 4,884,087 and 4,954,857 (corresponding to JP-A 64-544) is combined with a leader-advancing cassette, a problem still remains: the leader of the photo film cannot be advanced to the outside of a cassette shell due to the fold, even when the spool is rotated in an unwinding direction when treating the photo film cassette in a photo laboratory.
JP-A 61-156033 discloses a spool which is used for photo film and in which an edge of an entrance of a take-up slot formed through a spool core is rounded off by way of a curved face with a radius of curvature nearly 1/3 time as long as a radius of the core for the photo film. This curved face can prevent the leader from having a fold. However the inclined face is likely to cause the leader to have at irrecoverable curl. Once curled, the highly rigid photo film cannot recover its original condition without the curl. If the suggestion of JP-A 61-156033 is combined with a leader-advancing cassette, the problem still remains: the leader of the photo film cannot be advanced to the outside of a cassette shell due to the curl, even when the spool is rotated in an unwinding direction.